This invention relates to a synchronous belt and to a method for making the same.
A conventional synchronous belt, as described in Case, U.S. Pat. No. 2,507,852, has teeth of essentially trapezoidal cross-section which are similar to gear rack teeth. More recently, various changes in the contour or configuration of the belt tooth have been made. For example, Miller, U.S. Pat. No. 3,756,091 discloses a belt which includes driving teeth of a special curvilinear cross-sectional configuration. Another example is Gregg, U.S. Pat. No. 3,924,481 which discloses a belt having driving teeth of a special curvilinear cross-sectional configuration.
A problem which is common to virtually all synchronous belts is that of "tracking", i.e. the tendency of the belt to shift sideways during its rotation. It has been determined that a belt will tend to track in the direction of the lead of a spiralled tensile cord embedded therein. The tendency to track is also dependent upon cord twist.
One prior art solution to the tracking problem is found in Schmidt, U.S. Pat. No. 2,983,637, which discloses a synchronous belt having two layers of spiralled tension cords. The cords in the two layers are spiralled in opposite directions to form helices having an opposite inclination so that the longitudinal pull or tension is balanced and the tendency of the belt to creep sideways is diminished.
Since synchronous belts may be thought of as felt belts with transverse driving teeth, another prior art solution is found in Vance, U.S. Pat. No. 3,911,755 which discloses a single layer having oppositely twisted cords spiralled side-by-side at substantially the same angle in relation to the longitudinal axis of the belt. By placing the two cords side-by-side in the tensile section, each has an opposite influence on the tracking. There remains, however, the tracking effect of the spiral of the cords.
The most common solution to the tracking problem is merely to employ toothed pulleys having radial flanges which limit the sideways travel of the belt. Unfortunately, this simple solution may also introduce another problem, that being the problem of wear on the side face of the belt.
Accordingly, it is an object of the present invention to provide a synchronous belt having a reduced tracking tendency.
Another object of this invention is to provide a method for making a synchronous belt having a reduced tracking tendency.
Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the invention.